The task of keeping a good edge on skate blades is beset by a number of difficulties, which will now be described. Skate-blades have two knife edges, which run along the left and right sides of the blade. Usually, the region between the left and right knife edges is hollow, being ground to a concave curvature. Ice-skates are made in three main types: speed skates, figure skates, and hockey skates. The shape, length, and thickness of the blades of these types are somewhat different, but the left and right knife edges and the hollow grinding are a feature of most ice skates. Some types of speed skates are, however, sharpened flat, i.e. without the concavity between the knife edges, the reason being that some blades are so slim that hollow grinding would not be practical. If it were practical, however, hollow grinding would be preferred even with these very thin speed-skate blades.
It is important that the hollow grinding, if present, be maintained. Hollow grinding is important because a flat blade, when the blade was vertical during skating, would present a large surface area to the ice, and would skid if any lateral or sideways pushing against the blade were attempted.
It is also important that the two knife edges be straight and parallel, i.e. that both of the knife edges stand at the same height on the blade. Furthermore, there is little margin for error as regards the straightness and parallel-ness of the knife edges.
It is also important that, when the blade is being re-sharpened, the cutting motion takes place along the length of the blade. If the cutting or rubbing were to take place laterally with respect to the blade, the resulting cross-marks would give rise to a roughness, which would be quickly perceived by an expert skater.
Thus, if the skate blade is to be touched up by a rotating grinding wheel, it is necessary not only that the grinding machine include some means whereby the skate can be mounted most accurately, yet rigidly, relative to the grinding wheel; but it is also necessary that the wheel be set to rotate about an axis at right angles to the length of the blade; and it is also necessary that the wheel be kept accurately dressed to the correct curvature of the hollow region.
Such a grinding process as that just described requires, of course, a substantial apparatus--a fact which is no disadvantage as regards the task of sharpening the skate blade initially during manufacture of the skate, and the task of re-cutting the blade after the blade has suffered damage. But such a substantial apparatus is not really suited to the somewhat different task of touching-up a blade. Nevertheless, because of the absence of anything more appropriate, such grinding machines are in widespread use for touching-up.
There have been many proposals as to how the skate is to be located in the machine so that the knife edges are kept parallel, and so that only a minimum cut need be taken.
Following from the fact that the cutting force required to touch up the blade of a skate is quite small, it has been proposed, as an alternative to the grinding machine, to use a hand tool of the sharpening-stone type. The stone is held in the hand, and is rubbed to and fro along the length of the skate blade.
The problem with this and similar manual honing processes had been that the processes call for an extraordinary degree of skill on the part of the operator. It is all too easy for the operator to allow the stone to skew or wander sideways slightly, or to put more pressure on one knife edge than on the other. Besides the danger of spoiling the knife edges, operating a sharpening stone can be quite tiring to the muscles of the hand.
As mentioned, an expert skater is very sensitive to the slightest imperfections in the working surface of the blade. Accordingly, the touching-up of skate blades by the use of a hand-held stone is as a practical matter not available to the ordinary skater.
When skates have been reground on a grinding machine, it is possible to categorize three distinct states of the blade:
(1) just after re-grinding, the knife edges are too sharp, and the blades tend to dig into the ice rather too much, which can lead to strains and twists of the knees and ankles;
(2) once the knife-edges have settled down, the blade performs well;
(3) finally, the knife edges become dull and the blade starts to slip sideways when the skater pushes against the skate.
The second stage is quite short, so that the need arises for the skater to have the blades touched up at quite frequent intervals. But, if the skater uses the grinding machine method of touching up, he has to risk injury by going through the too-sharp first stage each time. Also, because the grinding machine has to take a sizeable cut each time it is used, the blade quickly becomes worn away.
Therefore, the general trend has been that a skater will wait until the knife edges become quite dull before having the blades touched up.
The invention is aimed at providing a sharpening tool in which the above problems and compromises are alleviated.